On March 20, a 44-year-old Liberian woman was diagnosed with Ebola. The case initially puzzled doctors because the epidemic had begun to wane in the country—her case was the first diagnosis in a month—and the woman hadn’t been to a funeral or in contact with any current patients.

The Centers for Disease Control confirmed that the woman’s case was likely the result of unprotected vaginal intercourse. The woman, the agency confirmed, had sex with an Ebola survivor, a 45-year-old man who had been free of the disease since October.

Although doctors have known for some time that the Ebola virus can survive in semen long after a patient is considered cured, there has never been a clear, documented case of this happening, according to the CDC report.

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But studies conducted during previous outbreaks have found that the Ebola virus can be found in semen up to 82 days after a patient’s initial symptoms.

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The CDC found genetic material, or RNA, from the Ebola virus in the man’s semen, nearly 200 days after he first contracted the disease. This is the longest period of time that scientists have detected the disease present in bodily fluids. It’s not yet known whether or not the man’s semen contains the live Ebola virus—though the CDC plans to continue testing.

The agency had previously advised survivors to abstain from sex or use condoms for three months after recovery. They have updated their guidelines, advising people to “avoid contact with semen from male survivors.”